In a work environment, the accumulated amount of noise, or dose in terms of an average noise level, and the maximum level of noise to which an individual has been exposed during a workday are important to occupational safety and to the health of the individual. Industrial and governmental agencies in countries throughout the world, such as the Occupational Safety and Health Administration (OSHA) in the United States, require accurate noise data measurements.
Examples of such noise data measurements include impulse noise, continuous noise, and an eight-hour time-weighted average (“TWA”). Impulse noise relates to noise of very short duration, less than a few thousandths of a second, which also repeats less than once a second. Continuous noise relates to noise that is longer in duration than impulse noise, e.g., extending over seconds, minutes, or hours. Eight-hour TWA relates to the average of all levels of impulse and continuous noise to which an employee is exposed during an eight-hour workday. The OSHA maximum level for impulse noise is 140 dBSPL measured with a fast peak-hold sound level meter (“dBSPL” stands for sound pressure level, or a magnitude of pressure disturbance in air, measured in decibels, a logarithmic scale). The maximum level for continuous noise is 115 dBA (read on the slow average “A” scale). OSHA regulations limit an eight-hour TWA to 90 dBA. If employees are exposed to eight-hour TWAs between 85 and 90 dBA, OSHA requires employers to initiate a hearing conservation program which includes annual hearing tests.
Among the many noise sources that are encountered in the workplace, measuring the exposure to noise related to telephone headsets is especially problematic. Telephone headsets generate their sound levels at or in the user's ear canal rather than external to the user. The external sound field levels referred to in many governmental regulations cannot be directly compared to these headset sound levels.
Also, headset users in the workplace typically have jobs requiring either that they spend a substantial amount of time on the phone, or that their hands be free to perform other tasks. Since the headset user's speaker is held in or against the user's ear, the user requires more time to respond to any irritating tones or noises by moving the speaker further away from the ear than one typically does with a regular telephone handset. Accordingly, workers can be exposed to sounds which may be irritating and even very loud. Such exposure is referred to in the art as “acoustic incidents.”
Claims of acoustic incidents by agents using headset equipment are investigated or defended by a number of actions which may include the measurement and examination of the telephone apparatus that was being used, the testimony of expert witnesses, and reference to recognized standards.
Some telephone equipment today may record agents' calls, but there is no calibrated reference level that allows someone examining an acoustic incident claim to determine the sound pressure level to which the agent was exposed. The sound pressure level to which the agent was exposed cannot be determined from a recording of the acoustic incident because conventional telephone call recordings are made not at the headset capsule interface but further back in the network path without any calibrated reference level being available for the recording. The result is that any recording may not actually represent what the agent heard, since it omits some of the signal chain/apparatus where the incident could have occurred (e.g., the telephone set, headset amplifier and headset), and since there is no reference to an absolute acoustic level.
A proposed solution to this problem is described in U.S. Pat. No. 6,507,650 to Moquin, entitled “Method for Noise Dosimetry in Appliances Employing Earphones or Headsets”. The Moquin patent discloses a system that estimates the sound pressure level within the headset amplifier, and records the estimate in a database. Sound pressure level is estimated by passing the audio waveform through a “system modeling filter,” which has a frequency response that models the transfer functions of the amplifier output stage, headset, artificial ear and A-weighting curve. Unfortunately, this estimation process is subject to inherent inaccuracies, has significant measurement error at some frequencies, and is unlikely to bear scrutiny by an expert witness skilled in acoustical measurements.
There is a need, therefore, for headset audio incident logging systems and methods that are more accurate and reliable than systems and methods available in the prior art.